A pvp nightblade is an assassin pretty much regardless what you do with them, lol. And stamblades are deadly in pvp right now. My main is a ganker. I'm not sure exactly what you're asking, though. Feel free to respond @ me if you have questions I don't cover.

Start with any of sypher's online stamblade builds. This is an excellent start.

Race: obviously any of the stam races. I like khajiit because they're sneakieR.

Gear: right now you can do a good bow build, or a good dual build for your attack bar. Hundings still reins Supreme as your first set, because you can craft and supplement pieces based on what youve been able to pick up for your second set.

For the second set, when using bow in pvp I like marksman...you should be able to get robust purple jewelry with a modest investment. If you just want to test, pick up blue jewelry for a couple thousand per piece and try before you invest in purple...the stat change is tiny. For Other sets, I like briarhearts (hard to get a set), vipers sting (not too expensive, but a bit) or morag tong. Depending on piece config, I sometimes supplement robust agility (very expensive) or a monster helm set or single piece. If you find yourself with one slot (like you're using two five piece sets with a bow build), grab a molag Kena shoulder for the great weapon damage boost.

Skills: I personally can't quite get away from 2h for my back bar because rally is just too dang powerful. I use this with dark cloak and vigor. The other two buttons are somewhat flexible. I use magelight a lot to get a 20% boost to the first gank attack (might of the guild). Rally + magelight + marksman from sneak can crit for 12-15k...it's a good start, lol. When I keep Defend on my bow, I slot propelling shield. It may sound weird, but with all my passives and that I get 50+ meters on my shots...usually people set up siege within this range and I can gank them from afar.

On my attack bar I like the standard ambush and surprise attack. I like piercing Mark as well for pvp. Focused aim on the bow build for sure, and poison arrows. On dual I sortmof go all over the place with the other weapons depending on how I want to play. The execute is good. Sometimes I use thenthrowing blade. Just depends. Note: with surprise attack I've always gone back and forth on the morph. There is no question that on a stam build SA does a LOT of spammable damage. However, if you can forego it and use something else, the speed boost from concealed weapon on the back bar can be very helpful for a sneak assassin.

The struggle right now with an assassin nightblade is that they are squishy. You have to establish your plan of attack and get in there to kill fast and efficiently. There's no real "one shotting" right now, so the key for me is to hit them as hard as possible with the first shot then get in there and keep them off guard. If they're a Templar, I have to kill them before they start casting heals and wards. For a sorc, before they ward. For a DK...figure out how tough they are and either finish the kill or run away.

Overall, assassin in pvp is one of my favorites right now. I kill from walls and towers during sieges with massive damage, or I go gank the highway supply lines. Stealth is a little nerfed from what it used to be, but it still works okay.